1. Technical Field
The present invention pertains to interconnections for microwave signals. In particular, the present invention pertains to coupling microwave signals from a removable microwave module installed on a chassis plate to a microstrip transmission line installed in the chassis plate.
2. Discussion of Related Technology
Microwave signals are typically processed and/or generated in microwave modules and coupled to microstrip transmission lines for signal transference and/or transmission. The microwave modules may be installed on a chassis plate, where the modules and chassis plate each contain a microstrip line. A conventional horizontal feedthrough approach of coupling microwave signals between the microwave module and a microstrip line on a chassis plate is illustrated in FIG. 1. Specifically, a microwave module 12 is installed on a chassis plate 10. The chassis plate includes a microstrip line 16, a microstrip channel 18 and a channel cover 20. Microwave module 12 is installed in a recessed section 22 of the chassis plate, while channel 18 is defined in a chassis plate raised portion adjacent the recessed section and houses microstrip line 16. Channel cover 20 is installed on the upper edges of channel 18 to cover the channel and enclose microstrip line 16 therein. Microstrip line 16 is typically laid into channel 18, where the channel is machined into chassis plate 10 to allow the channel to be covered and thereby electrically isolated from other microstrip transmission lines.
Microwave module 12 processes and/or generates microwave signals, where a feedthrough pin 14 is installed through the side wall of the microwave module adjacent channel 18. Feedthrough pin 14 extends into microstrip channel 18 and is substantially parallel to microstrip line 16. The feedthrough pin is attached, either directly or indirectly, to microstrip transmission line 16 mounted on the chassis plate within channel 18. The feedthrough pin serves to couple microwave signals processed and/or generated by microwave module 12 to microstrip line 16.
The configuration described above has several disadvantages. In particular, the conventional horizontal feedthrough approach described above provides a gap between the microwave module side wall and the covered channel containing the microstrip line. This gap produces signal leakage that can impact isolation of other signals on the chassis plate. Although gaskets may be utilized to impede signal leakage, this is problematic due to the need to establish horizontal pressure on the gasket in a vertical mounting direction and to maintain adequate pressure on the gasket over temperature variations in the presence of possibly differing coefficients of thermal expansion (CTE) (e.g., the fractional increase in length of an object for each degree of increased temperature) between the microwave module and chassis plate. Further, the gasket is required to maintain equal pressure on the vertical faces of both the chassis plate raised portion and the channel cover, thereby requiring the channel cover to be installed with high precision to align exactly with the edge of the chassis plate raised portion. Some mechanical configurations are commonly utilized to rectify this problem; however, these tend to complicate the feedthrough approach.
In addition, the gap creates an inductive ground discontinuity by forcing return currents to flow down the chassis plate raised portion face and up the face of the microwave module wall. The greater the height of the microwave module, the more severe the discontinuity. Although ground ribbons may be installed on either side of the feedthrough pin or conductive material may be placed to fill the gap in order to mitigate the ground discontinuity, these courses of action require complicated assembly and are not electrically ideal.